The present invention relates to arthroplastic reconstruction of the human joints and more particularly to flexible implant resection arthroplasty of the wrist joint.
Silicone implants have been successfully employed in the restoration of function of the joints of the hand which have been affected by rheumatoid arthritis and similar pathological conditions. The procedures developed to employ the silicone implants have generally been found to be more successful than prior attempts to restore motion. Such prior attempts have included soft tissue arthroplasties and the use of metal implants. The prior conventional operational procedures to correct deformities of the wrist joint were not wholly satisfactory in producing proper function of the wrist joint which is necessary for proper function of the hand.
Aseptic necrosis and/or arthritis of the carpal bones is a frequent cause of disability of the wrist joint. Surgical treatment of conditions of the wrist joint have heretofore included intercarpal fusion, wrist fusion, local resection, proximal row carpectomy, bone grafting, radial styloidectomy, radial shortening or ulnar lengthening, and soft tissue interposition arthroplasty. Fusion procedures are not completely acceptable since the stability, power and mobility of the wrist are affected, although pain is relieved. Local resection procedures involving the removal of an irreversibly pathological bone, are complicated by migration of adjacent carpal bones into the space left after the resection. This migration results in instability in the wrist joint. Metallic and acrylic implants developed for replacement of carpal bones have not been totally satisfactory due to problems relating primarily to progression of the arthritic process, migration of the implant, breakdown of the implant material and absorption of bone due to hardness of the material inserted.
Due to these shortcomings of such prior operative procedures, intramedullary stemmed silicone rubber implants have been developed to replace the scaphoid bone and the lunate bone of the carpal row. These implants were designed to act as articulating spacers capable of maintaining the relationship of adjacent carpal bones after excision of the lunate or scaphoid bone while preserving mobility of the wrist. Examples of such prior carpal bone implants may be found in Applicant's work entitled "Flexible Implant Resection Arthroplasty On The Hand And Extremities", 1973 by the C. V. Mosby Company. Also, an example of an improved lunate implant may be found in Applicant's copending application, Ser. No. 900,188, entitled LUNATE IMPLANT, and filed Apr. 26, 1978.
Initial attempts to develop carpal implants resulted in the implants having essentially the same anatomical shape as the bones being replaced. The prior scaphoid implant was developed through exhaustive anatomical shaping and sizing of cadaver bones and roentgenographic studies of a variety of hands. The prior scaphoid implant was provided in progressive sizes for either the right or left hand due to mirror image differences in the bone structures. The concavities of the scaphoid implant were more pronounced than those found in the bone being replaced since such was felt necessary to increase stability of the implant. A stabilizing stem was formed integral with the implant and fitted into the trapezium. The intramedullary stem maintained the position of the implant postoperatively until the capsuloligamentous system healed around the implant.
As previously stated, the prior scaphoid implant was essentially an anatomical replica of the bone being replaced. Over ten thousand measurements were made on a random selection of one hundred and twenty specimens of scaphoid bones. Angles were measured with a goniometer and a series of convex and concave patterns were employed to size the curved surfaces of the bones. A mean value was established for each dimension and proportioned implant sizes were fabricated. The resulting implants included multi-faceted, angled and curvilinear surfaces. The concavity of the implant which articulated about the capitate bone was, however, deepened. It was then believed that an anatomically correct implant including such deeper concavitities resulted in more stable arthroplastic reconstruction.